1. Field of the Invention
The present invention relates to a protective system for an electric unit powered by an exchangeable battery pack. The protective system prevents an unintentional restart of the electric unit after a change of the battery pack. The present invention also relates to an electric unit having such a protective system.
2. Description of the Related Art
Electrically operated units, such as a handheld machine tool, have to be supplied for the intended operation with the electrical power required for that purpose. For a network-independent and thus flexible use of such electric units, the power supply may take place using batteries. In the case of handheld machine tools, rechargeable batteries are frequently used, which are developed as compact battery packs. These battery packs, also known as accumulator packs, are mounted detachably in an appropriate accommodating device of the respective unit, in order to enable external charging or an exchange of the battery pack.
In order to connect the battery pack to the electric unit, contact elements that are complementary to each other are present on both parts. The contact elements form interfaces both to current supply of the electric unit and to a data exchange between battery and electric unit. During battery installation, the battery pack is pushed into the battery accommodating device of the electric unit, which causes the two parts to be connected to each other. As soon as the main contacts of the battery pack make contact with the main contacts on the electric unit, the current supply of the electric unit is established. If the main switch of the electric unit is already switched on at this point, the electric unit is activated upon installation of the battery pack, which is able to lead to an unintended restart. Furthermore, in this usual electric unit, spark formation may lead to typical manifestations of wear at the contact elements, since the contacting of the main contacts does not take place without current when the main switch is on.